Photoreconfigurable Supramolecular Nanotube

A photoreconfigurable bionanotube was developed by Mg2+-duced supramolecular polymerization using GroEL(SP), a mutant barrel-shaped chaperonin protein bearing multiple photochromic spiropyran (SP) units at its apical domains. Upon exposure to UV light, the nonionic SP units isomerize into ionic merocyanine (MC) to afford GroEL(MC), which is capable of polymerizing with MgCl2. The resultant nanotube (NT) is stable as a result of multiple MC center dot center dot center dot Mg2+center dot center dot center dot MC bridges but readily breaks up into short NTs, including monomeric GroEL(SP), by the reverse (MC -> SP) isomerization mediated by visible light. When this scission mixture is exposed to UV light, long NTs are reconfigured. A Forster resonance energy transfer (FRET) study revealed that NTs in the dark maintain their sequential integrity. However, when exposed to visible and UV light successively, the NTs lose their sequential memory as a result of intertubular reshuffling of the constituent GroEL(MC) units.